Squalene Monooxygenase Gene <i>SsCI80130</i> Regulates <i>Sporisorium scitamineum</i> Mating/Filamentation and Pathogenicity

Sugarcane is an important sugar crop and energy crop worldwide. Sugarcane smut caused by <i>Sporisorium scitamineum</i> is a serious fungal disease that occurs worldwide, seriously affecting the yield and quality of sugarcane. It is essential to reveal the molecular pathogenesis of <i>S. scitamineum</i> to explore a new control strategy of sugarcane smut. Based on transcriptome sequencing data of two <i>S. scitamineum</i> strains <i>Ss16</i> and <i>Ss47</i>, each with a different pathogenicity, our laboratory screened out the <i>SsCI80130</i> gene predicted to encode squalene monooxygenase. In this study, we obtained the knockout mutants <i>(ΔSs80130⁺</i> and <i>ΔSs80130</i>⁻) and complementary mutants (<i>COM80130</i>⁺ and <i>COM80130</i>⁻) of this gene by the polyethylene glycol-mediated (PEG-mediated) protoplast transformation technology, and then performed a functional analysis of the gene. The results showed that the deletion of the <i>SsCI80130</i> gene resulted in the increased content of squalene (substrate for squalene monooxygenase) and decreased content of ergosterol (the final product of the ergosterol synthesis pathway) in <i>S. scitamineum</i>. Meanwhile, the sporidial growth rate of the knockout mutants was significantly slower than that of the wild type and complementary mutants; under cell-wall stress or oxidative stress, the growth of the knockout mutants was significantly inhibited. In addition, the sexual mating ability and pathogenicity of knockout mutants were significantly weakened, while the sexual mating ability could be restored by adding exogenous small-molecular signal substance cAMP (cyclic adenosine monophosphate) or tryptophol. It is speculated that the <i>SsCI80130</i> gene was involved in the ergosterol biosynthesis in <i>S. scitamineum</i> and played an important role in the sporidial growth, stress response to different abiotic stresses (including cell wall stress and oxidative stress), sexual mating/filamentation and pathogenicity. Moreover, the <i>SsCI80130</i> gene may affect the sexual mating and pathogenicity of <i>S. scitamineum</i> by regulating the ergosterol synthesis and the synthesis of the small-molecular signal substance cAMP or tryptophol required for sexual mating. This study reveals for the first time that the gene encoding squalene monooxygenase is involved in regulating the sexual mating and pathogenicity of <i>S. scitamineum</i>, providing a basis for the molecular pathogenic mechanism of <i>S. scitamineum</i>.